FullscreenUI: Prefetch two rows of covers in grid view

Less change of loading/placeholder images.

src/core/fullscreenui_achievements.cpp

@@ -2164,8 +2164,6 @@ void FullscreenUI::DrawAchievement(const rc_client_achievement_t* cheevo, const
                                (is_measured ? (spacing + LayoutScale(progress_height_unscaled)) : 0.0f) +
                                LayoutScale(LAYOUT_MENU_ITEM_EXTRA_HEIGHT);
 
-  const float pos_y = ImGui::GetCursorPosY();
-
   SmallString text;
   text.format("chv_{}", cheevo->id);
 
@@ -2174,6 +2172,7 @@ void FullscreenUI::DrawAchievement(const rc_client_achievement_t* cheevo, const
   const bool clicked = MenuButtonFrame(text, content_height, true, &bb, &visible, &hovered);
   if (!visible)
   {
+    const float pos_y = ImGui::GetCursorPosY();
     if (pos_y >= prefetch_range.x && pos_y <= prefetch_range.y)
     {
       if (const std::string_view badge_url = Achievements::GetAchievementBadgeURL(cheevo, !is_unlocked);

src/core/fullscreenui_game_list.cpp

@@ -775,6 +775,10 @@ void FullscreenUI::DrawGameGrid(const ImVec2& heading_size)
   if (!s_game_list_locals.game_list_sorted_entries.empty())
     ImGui::SetCursorPosX(ImGui::GetCursorPosX() + x_padding);
 
+  // Prefetch two rows worth of covers.
+  const ImVec2 prefetch_range =
+    ImVec2(window->Pos.y + window->Scroll.y, window->Pos.y + window->Scroll.y + (window->ClipRect.GetHeight() * 2.0f));
+
   for (size_t entry_index = 0; entry_index < s_game_list_locals.game_list_sorted_entries.size(); entry_index++)
   {
     if (window->SkipItems)
@@ -861,6 +865,11 @@ void FullscreenUI::DrawGameGrid(const ImVec2& heading_size)
         HandleGameListOptions(entry);
       }
     }
+    else
+    {
+      if (pos.y >= prefetch_range.x && pos.y <= prefetch_range.y)
+        GetGameListCover(entry, false, false, false);
+    }
 
     if (entry == s_game_list_locals.game_list_sorted_entries.front())
       ImGui::SetItemDefaultFocus();